Normal hearing individuals are capable of selectively paying attention to achieve speech intelligibility and to maintain situational awareness under noisy listening conditions such as restaurants, bars, concert venues etc. so-called cocktail party scenarios or sound environments. Normal hearing individuals are capable of utilizing a better-ear listening strategy where the individual focuses his or her attention on the speech signal of the ear with the best signal to noise ratio for the target talker or speaker, i.e. a desired sound source. This better-ear listening strategy can also allow for monitoring off-axis unattended talkers by cognitive filtering mechanisms, such as selective attention.
In contrast, it remains a challenging task for hearing impaired individuals to listen to a particular, desired, sound source in such noisy sound environments and at the same time maintain environmentally awareness by monitoring off-axis or unattended talkers. Hence, it is desirable to provide similar hearing capabilities to hearing impaired individuals for example by exploiting well-known spatial filtration capabilities of existing binaural hearing aid systems. However, the use of binaural hearing aid systems and associated beamforming technology often focuses on increasing or improving a signal to noise ratio (SNR) of a bilaterally or binaurally beamformed microphone signal or signals for incoming sounds at a particular target direction, often in the frontal direction of the individual, at the expense of decreasing the audibility of the unattended, often off-axis located, talkers in the sound environment. The signal to noise ratio improvement of the binaurally beamformed microphone signal is caused by a high directivity index of the binaurally beamformed microphone signal which means that sound sources placed outside a relatively narrow angular range around the selected target direction are heavily attenuated or suppressed. The narrow angular range wherein sound sources remain substantially unattenuated may extend merely +/−20-40 degrees azimuth around the target direction. This property of the binaurally beamformed microphone signal leads to an unpleasant so-called “tunnel hearing” sensation for the hearing impaired individual or patient/user where the latter loses situational awareness.
There is a need in the art for binaural hearing aid systems which provide hearing impaired individuals with improved speech intelligibility in cocktail party sound environments, or similar adverse listening conditions, but without sacrificing off-axis awareness to provide increased situational awareness relative to prior art comparable directional hearing aid systems.
U.S. Pat. No. 8,755,547 discloses a binaural beamforming method and binaural hearing aid system for enhancing the intelligibility of sounds. The method of enhancing intelligibility of sounds includes the steps of: detecting primary sounds emanating from a first direction and producing a primary signal; detecting secondary sounds emanating from the left and right of the first direction and producing secondary signals; delaying the primary signal with respect to the secondary signals; and presenting combinations of the signals to the left and right sides of the auditory system of a listener. U.S. Pat. No. 8,755,547 utilizes the precedence effect for localization dominance only.